runLinter() fails very frequently on Linux

[jakepetroules]

Describe the bug
Running this test results in the swift-format process never exiting (it shows it's stuck in writing to stderr). Closing the parent file descriptors after the call to captureIOs() seems to work around this, but I don't think that's correct and I'm not sure what's going on here.

To Reproduce
swift test --filter runLinter()

Expected behavior
Test does not hang.

Environment (please complete the following information):

• Linux debian 6.1.0-31-arm64 #\1 SMP Debian 6.1.128-1 (2025-02-07) aarch64 GNU/Linux
• Debian GNU/Linux 12.9 (bookworm)
• Swift version 6.1 (swift-6.1-RELEASE)
• Target: aarch64-unknown-linux-gnu

Additional context
Add any other context about the problem here.